Metamorphic Properties And Chronology Of Feidong Massif In The Middle Of Tan-lu Fault

The Feidong terrane (FDT) located at the the middle part of Tanlu fault (TLF), and the accurate determination of its metamorphic evolution and tectonic attribution is key to probe into the formation of the TLF. Up to now, the regional metamorphic study on the FDT still is sparsity that directly restricts the understanding for the origin of the TLF.In this study, the systematic fieldtrip survey, regional metamorphic study, thepetrologcial anaylsis, and the thermodynamic appraise have been carried out across the FDT. The research is divided into two parts. One is the analysis forregional metamorphic petrology and geochronology across the FDT. The other is the discovery of Jurassic granite, garnet-biotite schist and magnetic-gernet amphibolite which may from North China Plate.(1) The study indicates that the FDT is composed of Unit-I, II and III fromwest to east, and include granitic gneiss, biotite-plagiclase gneiss, amphibole-plagiclase gneiss, some amphibolite and garnet-biotite-plagiclase gneiss. The P-Testimates of amphibolite and garnet-biotite-plagiclase gneiss show that the peakmetamorphic conditions for the FDT are in the range of610~690℃and0.61~0.81GPa, and average P-T conditions are656±25℃and0.71±0.06GPa, whichplot in the amphibolite faces. The U-Pb age of zircons from the amphibolitesis809.2±6.7Ma, which suggests that the FDT have origin of the Yangtze Plate. Combined with the structural analysis and geochronologcial data from the previous studies, the FDT should be equal to the Susong complex rocks, the present P-T discrepancy between them is due that the TLF with sinisral slip offsets this corresponding stratum during subduction.(2) Preliminary studies have confrimed that the Unit-III contains a little of the garnet-biotite schist and magnetite-garnet amphibolite as lens. Meanwhile thedeformed granite during Jurassic has been determined. The results of this study indicate that the magnet-garnet amphibole and the associated rock is the tectonic lens. The P-T estimates shows that these rocks had been underwent two-stage metamorphism and displayed a rapid and slight Isobaric cooling process. The U-Pb ages of metamorphic zircon for the garnet-biotite schist and magnet-garnet amphibole are2406±28Ma and2469±49Ma respectively. These ages are inaccordance with the~2.5Ga geological event of North China Plate partially. T his implies that these rocks may be come from north china plate, which located in the FDT due to the sinistral strike-slip of Tan-Lu Fault Zone. The age ofdeforamtion granite as Jurassic intrusive rock is167.7±4.6Ma. This granite isoutcropping in Yangtze plate rarely. However, the mechanism for the granite isunclear due to unsufficient investigation in this study, and more research stillhave been carried out in future.